Fix possible protocol desync with SchemaOnly and auto prepare (#5221)

Fixes #5220 (cherry picked from commit 8c0e93b)
npgsql · Aug 25, 2023 · 8060929 · 8060929
1 parent 29d9395
commit 8060929
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Showing 2 changed files with 12 additions and 8 deletions.
diff --git a/src/Npgsql/NpgsqlDataReader.cs b/src/Npgsql/NpgsqlDataReader.cs
@@ -728,20 +728,21 @@ async Task<bool> NextResultSchemaOnly(bool async, bool isConsuming = false, Canc
                     default:
                         throw Connector.UnexpectedMessageReceived(msg.Code);
                     }
+
+                    if (_statements.Skip(StatementIndex + 1).All(x => x.IsPrepared))
+                    {
+                        // There are no more queries, we're done. Read to the RFQ.
+                        Expect<ReadyForQueryMessage>(await Connector.ReadMessage(async), Connector);
+                    }
                 }
 
                 // Found a resultset
                 if (RowDescription != null)
                     return true;
             }
 
-            // There are no more queries, we're done. Read to the RFQ.
-            if (!_statements.All(s => s.IsPrepared))
-            {
-                Expect<ReadyForQueryMessage>(await Connector.ReadMessage(async), Connector);
-                RowDescription = null;
-                State = ReaderState.Consumed;
-            }
+            RowDescription = null;
+            State = ReaderState.Consumed;
 
             return false;
         }

diff --git a/test/Npgsql.Tests/AutoPrepareTests.cs b/test/Npgsql.Tests/AutoPrepareTests.cs
@@ -542,7 +542,7 @@ public async Task Batch_statement_execution_error_cleanup()
         Assert.That(await conn.ExecuteScalarAsync("SELECT 3"), Is.EqualTo(3));
     }
 
-    [Test, IssueLink("https://github.com/npgsql/npgsql/issues/4404")]
+    [Test, IssueLink("https://github.com/npgsql/npgsql/issues/4404"), IssueLink("https://github.com/npgsql/npgsql/issues/5220")]
     public async Task SchemaOnly()
     {
         var csb = new NpgsqlConnectionStringBuilder(ConnectionString)
@@ -559,6 +559,9 @@ public async Task SchemaOnly()
         {
             await using var reader = await cmd.ExecuteReaderAsync(CommandBehavior.SchemaOnly);
         }
+
+        // Make sure there is no protocol desync due to #5220
+        await cmd.ExecuteScalarAsync();
     }
 
     [Test]